A selective call system provides transmission of selective call messages from a message originator to a selective call receiver. The originator contacts a selective call terminal and provides the content of the message and information identifying the intended receiver thereto. The selective call terminal encodes the message into one of several known protocols, such as the POCSAG signalling code. In addition, the terminal appends an address assigned to the selective call receiver to the message. The address and message are then modulated onto a selective call signal and transmitted from the selective call terminal. When the selective call receiver recognizes its address within the selective call signal, the message therefollowing is demodulated and decoded.
It is more economical for a selective call system service provider to have denser selective call traffic (i.e., a greater number of messages transmitted per hour). Therefore, if a single message is to be transmitted to a number of selective call receivers, the option of group calling is appealing to the service provider. There are two types of group calling: radio group calling and terminal group calling. Radio group calling requires an additional group address to be permanently assigned to receivers within a group. Radio group calling provides the greatest savings in air time in that a single address and message can be provided to multiple receivers within a group. Yet, radio group calling is inflexible. To change the receivers assigned to the group, the receivers would need to be reprogrammed to remove or add the group address.
Terminal group calling is more dynamic in that the members of the group can be defined at the terminal as a message is prepared for transmission. One example of terminal group calling is the multiple addressing of voice messages in the Golay Sequencing Code signalling protocol. Yet, terminal group calling does not result in substantial air time savings for the service provider. At a minimum, multiple addresses need to be transmitted from the terminal and, in some terminal group calling schemes, the message also needs to be sent a number of times.
Thus what is needed is a method and apparatus for dynamic group calling allowing for the receivers assigned to a group to be easily reassigned while providing substantial savings in air time.